SCHEDULE 13G/A 0001193125-24-258671 0001224962 XXXXXXXX LIVE 3 Common Stock, par value $0.001 per share 03/31/2025 0001786205 Arcellx, Inc. 03940C100 800 Bridge Parkway Redwood City CA 94065 Rule 13d-1(d) Perceptive Advisors LLC DE 0 2926478 0 2926478 2926478 N 5.3 IA Joseph Edelman X1 0 2926478 0 2926478 2926478 N 5.3 IN Perceptive Life Sciences Master Fund, Ltd. E9 0 2926478 0 2926478 2926478 N 5.3 CO Arcellx, Inc. 800 Bridge Parkway, Redwood City, CA 94065 The names of the persons filing this report (collectively, the "Reporting Persons") with respect to shares of Common Stock, par value $0.001 per share (the "Common Stock") of Arcellx, Inc. (the "Issuer") are: (i) Perceptive Advisors LLC ("Perceptive Advisors") (ii) Joseph Edelman ("Mr. Edelman") (iii) Perceptive Life Sciences Master Fund, Ltd. (the "Master Fund") The address of the principal business office of each of the Reporting Persons is: 51 Astor Place, 10th Floor, New York, NY 10003 Perceptive Advisors is a Delaware limited liability company. Mr. Edelman is a United States citizen. The Master Fund is a Cayman Islands corporation. Y The information required by this item with respect to each Reporting Person is set forth in Rows 5 through 9 of the cover pages to this Schedule 13G. The ownership percentages reported are based on 55,072,693 shares of Common Stock outstanding as of April 4, 2025, as reported in the Issuer's Definitive Proxy Statement on Schedule 14A filed with the Securities and Exchange Commission on April 17, 2025. The Master Fund directly holds 2,926,478 shares of Common Stock. Perceptive Advisors serves as the investment manager to the Master Fund. Mr. Edelman is the managing member of Perceptive Advisors. Perceptive Advisors: 5.3% Mr. Edelman: 5.3% Master Fund: 5.3% Perceptive Advisors: 0 Mr. Edelman: 0 Master Fund: 0 Perceptive Advisors: 2,926,478 Mr. Edelman: 2,926,478 Master Fund: 2,926,478 Perceptive Advisors: 0 Mr. Edelman: 0 Master Fund: 0 Perceptive Advisors: 2,926,478 Mr. Edelman: 2,926,478 Master Fund: 2,926,478 Y Y Y Y Y Y Perceptive Advisors LLC /s/ Joseph Edelman 05/15/2025 Joseph Edelman /s/ Joseph Edelman 05/15/2025 Perceptive Life Sciences Master Fund, Ltd. /s/ Joseph Edelman 05/15/2025